1. Field of the Invention
The present invention relates to a control method and a controller that control an addition valve that supplies an additive to the exhaust passage of an internal combustion engine. The control method and the controller intermittently add an additive that suppresses clogging of the addition valve.
2. Description of the Related Art
The exhaust system of some internal combustion engines is provided with an exhaust purifying member such as a carrier that carries a NOx purifying catalyst that purifies NOx (nitrogen oxide), a PM filter for collecting particulate matter in exhaust gas, or a DPNR catalyst having a NOx purifying catalyst carried on a PM filter.
An additive is often supplied to such an exhaust purifying member for the purpose of recovering its purifying function. For example, by supplying fuel as such an additive to a PM filter on which a NOx purifying catalyst is carried, NOx absorbed by the catalyst is reduced/released to recover the NOx purifying function of the NOx purifying catalyst. Also, particulate matter collected by the PM filter is burnt.
When the additive is supplied from an addition valve provided in the exhaust passage of an internal combustion engine, the distal end portion of the addition valve is exposed to high-temperature exhaust gas. Thus, additive remaining in the inner portion of the distal end of the addition valve often solidifies, thereby clogging of the addition valve. Also, clogging may also occur when particulates such as soot enter and adhere to the inner portion of the distal end of the addition valve.
Accordingly, in the technique described in Japanese Patent Application Publication No. 2003-222019 (JP-A-2003-222019), for example, in addition to adding additive to recover the function of an exhaust purifying member, the additive is added intermittently to suppress clogging of the addition valve described above.
In the device described in JP-A-2003-222019, the additive is added before the additive remaining at the distal end portion of the addition valve solidifies, thus optimizing the interval of addition when executing intermittent addition. On the other hand, the amount of additive added when executing intermittent addition is set to an amount that is neither too large nor too small in suppressing occurrence of clogging. However, there are cases where the addition amount is too much or too small in suppressing occurrence of clogging despite of the above addition control.